Increase in cytoplasmic free Ca 2+ elicited by noradrenalin and serotonin in cultured local interneurons of mouse olfactory bulb

Abstract

Effects of noradrenalin and serotonin on cytoplasmic free Ca 2+ concentrations ([Ca 2+] i) were studied by using the fluorescent indicator fura-2 in cultured local interneurons of mouse olfactory bulb. Application of noradrenalin (0.1–100 μ M) caused a rapid and concentration-dependent rise in [Ca 2+] i, while isoproterenol was ineffective at concentrations up to 100 μM. The noradrenalin (1 μM)-induced increase in [Ca 2+] i was completely inhibited by pretreatment with α 1-antagonist, prazosin (100 nM), whereas the inhibitory effect of α 2-antagonist, yohimbine, was about 100-times less potent. Serotonin (0.1–100 μM) also caused the dose-dependent rise in [Ca 2+] i, which was inhibited by serotonin 2 antagonist, ketanserin. Even in the absence of the extracellular calcium, the noradrenalin- or serotonin-induced increase in [Ca 2+] i was observed. These results indicate that both noradrenalin and serotonin elicit the rise in [Ca 2+] i in local interneurons of the olfactory bulb. They also suggest that the rise in [Ca 2+] i is mediated by α 1-adrenergic and serotonin 2 receptors, and that the increased calcium is mainly derived from intracellular calcium storage sites. The above results provide evidence to suggest that in the olfactory bulb, noradrenergic and serotonergic centrifugal fibers exert modulatory influences on synaptic interactions between mitral/tufted cells and local interneurons by increasing cytoplasmic Ca 2+ in local interneurons.